import paddle.fluid as fluid

x1 = fluid.layers.fill_constant(shape=[2, 2], value=1, dtype="int64")
x2 = fluid.layers.fill_constant(shape=[2, 2], value=1, dtype="int64")
y1 = fluid.layers.sum(x=[x1, x2])
place = fluid.CPUPlace()
exe = fluid.executor.Executor(place)
exe.run(fluid.default_startup_program())
# result = exe.run(program=fluid.default_main_program(), fetch_list=[y1])
# print(result)

AttributeError: 'NoneType' object has no attribute 'get_fetch_list'